Ozonation system for treatment of water in cooling towers

ABSTRACT

An improved system for treatment of cooling tower water using ozone as a biocide. A self-contained unit is supplied with compressed air which is introduced to ozone generating electrodes at a constant flowrate. The ozone is mixed with tower water and then returned to the cooling tower. A sampling probe allows for constant monitoring of the ozone content of water coming from the tower. The volume of ozone mixing with the tower water is accordingly constantly adjusted. The system also includes safety control features to monitor system operation and provide shutoff in the event of malfunction.

BACKGROUND OF THE INVENTION

1. Introduction

This invention relates to an improved ozonation system for treatment ofcooling tower water typically utilized in conjunction with the operationof large-scale cooling and air-conditioning equipment and, moreparticularly, pertains to significant advances in the efficientoperation of an ozone generation system keeping it at optimal operationcondition, protecting the ozonation system, and informing others ofproblems within the system.

2. Prior Art

Ozone has been used in the treatment of drinking water for more than 100years. While there is much literature on the subject, the more modernwork done with ozone is summarized in an article by Maurice Ogden ofWater Treatment Corp. appearing in the June, 1970 issue of "IndustrialWater Engineering". This article discusses the use of ozone to treatwater. It mentions an ozone treatment plant built and put into operationin 1949 by the Philadelphia Water Works, and reviews advances inacid-resistant materials for air conditioning systems and breakthroughsin electrical circuitry design allowing for the development of a moreefficient ozone generating unit.

U.S. Pat. No. 4,172,789, issued Oct. 30, 1979, discloses the type ofstructure described in the above article, namely a water tower withmeans to generate ozone, mix the water tower water with the generatedozone, and then return the ozone enriched water to the tower.

H. Banks Edwards discusses the use of ozone as "an alternate method oftreating cooling tower water" in the Journal of the Cooling TowerInstitute, Vol. 8, No. 2, 1987, page 10. Edwards illustrates a moresophisticated cooling tower than that of the '786 patent. The articlediscloses dividing the water coming from the tower so a sample portiongoes back into the tower while the remaining portion is ozone enriched.

A paper was presented on "Ozone Treatment of Cooling Water: Results of aFull-Scale Performance Evaluation" at the 1989 Cooling Tower InstituteAnnual Meeting by G. Darell Coppenger, Benjamin R. Crocker, and David E.Wheeler. The paper also verified the many benefits of oxygenation. Itshows (FIG. 3, page 21) the use of a personal computer to operate thesystem and means to monitor the quality of the water and the voltagepotential across an ozone sensing probe.

Further developments are illustrated in the catalog of OzonairInternational Corp. of South San Francisco, Calif., which illustratesspecially designed sensor electrodes with solid state and transistorizedcircuitry. Another sophisticated example is the ozone self-containedinjection system of Prosys of Chelmsford, Mass.

All of these systems, while feasible and performing in the field, do notdevelop a sufficient volume of ozone for the number of electrodes. Theydo not provide true commercial benefits.

OBJECTS AND ADVANTAGES OF THE PRESENT INVENTION

A principal object of the present invention is to provide a new andimproved ozonation system to treat cooling tower water.

Another object of the present invention is to provide a self-containedozonation unit with an advanced electrode design capable of providingsubstantially increased levels of ozone at a reduced cost.

Yet another object of the present invention is to provide an ozonationunit with the ability to monitor the ozone levels in water leaving thecooling tower and adjust the amount of ozone entering the system on acontinuous basis.

Still another object of the present invention is to provide a unit ofthe character described having a control system which constantly testvarious parameters of the system, to provide appropriate signals upondevelopment of operational problems.

Still a further object of the present invention is to make an ozonetreatment system which is practical in operation.

Still another object of the present invention is to provide a uniquedesign of electrode which is comparable in dimensions to currentelectrodes but results in vastly improved ozone generating efficiency.

Still yet a further object of the present invention is to provide a unitof the character described which is inexpensive and simple tomanufacture and yet durable in use.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

The present invention consists of a self-containedmicroprocessor-controlled ozonation unit incorporating a uniqueozone-generation electrode. A first air inlet supplies compressed air atapproximately 100 psi which is filtered and dried, resulting in a highlydepressed dewpoint. The filtered and dried air is dropped in pressurefrom 100 psi to approximately 3 psi, the dewpoint correspondinglydropping to about -140° to -160° F. The air then passes through aflowmeter which controls the volume of air directed to ozone-generatingelectrodes of the unit. The electrodes excite the oxygen in the air fromits stable form (O₂) to its unstable (O₃) ozone form.

The unique electrode consists of a central electrical connecting rodwhich is supported by insulating inserts at its proximal end pointswithin a cylindrical metallic outer tube. An inner concentric conductortube is electrically connected to the central connector rod. A tubularsilicon dielectric material is placed between the inner and outer tubesand is spaced from the outer tube. The inner surface of the outer tubeand the outer surface of the silicone dielectric form an air gap acrosswhich a high voltage potential is placed, causing corona discharge whichconverts the oxygen in the air gap to the ozone form.

Air is introduced into the electrode air gap by means of a series ofholes which, in conjunction with the construction of the dielectric,cause a spiral air flow through the electrode. Because of this spiralflow, the air remains within the electrode for a greater length of timethan with a direct flow, allowing for a greater degree of ozoneproduction. The air exits the electrode through a similar arrangement ofholes at the second end. The ozone enriched air that emerges from theelectrode carries approximately 500 percent more ozone than similarlydimensioned prior art structures.

The computer-based control system includes an oxidation-reductionpotential (ORP) probe which monitors the ORP level of the tower water. Acontroller adjusts the voltage applied to the electrodes on a continuousbasis to provide a varying ozone production. The ozone production levelis proportional to the oxidation-reduction potential sensed by the ORPprobe, such that the ORP of the water, which is indicative of the levelof all oxidants present in the water including ozone, ozonides,secondary biocides, chlorine present in the make-up water, aldehydes andthe like, is maintained at a proper level. The system also monitors theprotective devices of the unit, issuing appropriate alarm signals whenan out-of-range condition is experienced. The alarm signals may bebroadcast both locally and remote to the system.

When the ORP is in the proper range, as maintained by the presentsystem, organic material present as water contaminants in the system,which can cause the attachment of scale to the fluid contacting surfaces(tower, lines, etc.) of the air conditioning/cooling system to which thewater supply is connected, are effectively and continuously oxidized andrendered incapable of fouling the system. The water system thus canoperate for longer periods without maintenance and without the necessityof flushing and disposal of accumulated sludge.

In distinction to the prior art, the present invention provides an ozonelevel of 0.03 to 0.07 ppm, which allows secondary biocides, such asaldehyde soaps formed from the reaction between ozone and contaminantsin the water, to remain active. This maintains a positive residual forseveral days in the event of system shutdown. By maintaining an ORP inthe range of 550-650, offgassing of ozone from the water which occurs atelevated ORP levels is avoided, thus providing improved environmentalbenefits and eliminating the risk of corrosion due to the effects ofozone gas.

The water subject to treatment is drawn from the cooling system's watertower by a pump and is divided, a portion of which being directed to aventuri which draws the ozone-enriched air exiting from the electrodesinto a venturi and blends the air and water portion together. Theair-water blend is combined with the remaining portion of the drawnwater by a motionless mixer, and is returned to the water tower. The ORPprobe constantly monitors the untreated water portion to ascertain theORP and thus the level of total oxidants present, the system constantlyadjusting the electrode voltage, either reducing, increasing, orstopping ozone production as required to maintain the monitored water atthe correct ozone level.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a unit comprising our invention;

FIG. 2 is rear elevational view of the same unit;

FIG. 3 is a schematic showing the principal mechanical elements withinthe unit;

FIG. 4 is a schematic of the electrical elements within the unit;

FIG. 5 is a block diagram of an inverter used in the invention;

FIG. 6 is a side elevational view of an electrode, partly in section andpartly cut away;

FIG. 7 is an enlarged cross sectional view of the left end of theelectrode taken along the line 7--7 of FIG. 6;

FIG. 8 is an enlarged cross sectional view of the right end of theelectrode taken along the line 8--8 of FIG. 6;

FIG. 9 is an enlarged cross sectional view of the arrangement of theholes at the left end of the electrode taken along the line 9--9 of FIG.7;

FIG. 10 is a schematic showing air travel through the electrode;

FIG. 11 is a cross sectional view taken along the line 11--11 of FIG. 6;

FIG. 12 is an enlarged cross-section view of the central portion of theelectrode detailing the connection between the central rod and innertube;

FIG. 13 is a further enlarged cross-sectional view showing the structureof the electrode air gap; and

FIG. 14 is a block diagram of the controller of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning in detail to the drawings and initially to FIGS. 1 and 2, thereis shown an ozonation treatment unit 10 containing our new improvedozone generator. The cabinets 12, 14 and 16 house the electricalcomponents required for system operation. The cabinets and associatedmechanical gear are mounted on a stand and pedestal frame 18. Theelectrodes (not shown) which produce the ozone are mounted horizontally,while the water to be treated is pumped by pump 22 and is treated withinthe piping generally indicated a 24. Protective gratings 26 are utilizedas required to further isolate portions of the apparatus.

As shown in the flow diagram of FIG. 3, atmospheric air is compressed bycompressor 28 up to approximately 100 psig at a 5 scfm flow rate. Thecompressed air is then delivered to a pressure regulator 30 and then towater pre-filter 32 to remove the bulk of the moisture from thecompressed air. The treated air is then passed through oil removalpre-filter 34. Both the pressure regulator and the filters are availablefrom SMC Lakewood, N.J. The double-treated air, still at approximately100 psi, is then passed to a heatless regenerative air dryer 36. Thedryer contains a desiccant which purges itself approximately every fourminutes, such as the Model No. DWH-5, manufactured by Hankison ofPittsburgh, Pa. At this point the air is still at 100 psi, but it has a-100° F. dewpoint.

The dried air is then passed through after-filter 38 which removes anydust and particulate matter that the air may have picked up from thedesiccant in the air dryer 36. The after filter may be the SMC Model No.NAFD3000-NO. 3. Pressure regulator 40 then drops the pressure from 100psi to approximately 3 psi. The dewpoint also drops to between -140° to-150° F. An acceptable regulator is also available from SMC as Model No.R05-02-000.

Flowmeter 42 controls the volume of air directed to the electrodes 20.The number of electrodes may be varied depending on the volume of air tobe treated. The flow rate through the electrodes is constant,irrespective of the level of ozone produced. A typical flowmeter is madeby Dwyer of Michigan City, Ind., Model No. RMA-9-SSV. There may be four,eight or twelve electrode assemblies 20, depending upon how much ozonehas to be produced to properly treat the volume of water in the watertower. The ozone-enriched air exits the electrodes via a conduit 44 aswill be explained.

A water pump 22 draws water from the water tower 46 via a conduit 48.The water exits pump 22 via conduit 50 to a venturi nozzle 52 where thewater is accelerated, the resulting pressure drop drawing theozone-enriched air in from the conduit 44. A typical venturi ismanufactured by Mazzi of Bakersfield, Calif., under Model No. 1584A(Kynar). A portion of the water from the tower 46 bypasses the venturivia conduit 54 and rejoins the ozone-enriched water at connection 56.The combined stream passes into a motionless mixer 58 to ensure completedispersal of the ozone throughout the water. An acceptable mixer ismanufactured by Koflo of East Dunder, Ill., Model No. 11/2-80-4-3U.-1.Treated water is then returned to the water tower 46.

One of the principal features of invention is the novel structure forthe ozone generator electrode assemblies 20. As can be seen in FIGS.6-13, the ozone generator consists of a plurality of electrodes 20 eachhaving an outer tube 60 with a left proximal end 62 detailed in FIG. 7and a right distal end 64 detailed in FIG. 8. Positioned within andspaced from the inner surface 66 of the outer tube is a silicone tube 68(FIGS. 6 & 7) defined by an outer surface which is formed of wrappedfiberglass and silicone stripping 70 (FIG. 13) defining a spiralconfigured leading edge or step 72 advancing diagonally to the upperright through the electrode as seen in FIG. 6. This spiral edge causesthe air to travel in a swirling pattern as it travels through theelectrode, as depicted in FIG. 10, thus increasing residence time in theelectrode. A Flex tab 7701-150 silicone Turbo Tube is preferred for useas the tube 68.

The outer tube 60 and silicone tube 68 are so dimensioned as to leave agap 74 between the outer tube inner surface 66 and the silicon tubespiral wrap outer surface 70, as best seen in FIGS. 11 and 13. The gapvaries somewhat because of the spiral wrapping, but it averages slightlyless than 1/16 of an inch. It has been found this provides a maximumefficiency for the production of ozone, although it may not be the onlycommercially acceptable width.

Positioned within tubes 60, 68 and having an axis concentric with bothtubes is a center, inner tube 76 (FIG. 7), having an outer surface 78. Asolid metallic center plug 80 (FIG. 12) is positioned within the centertube 76 and includes a coaxial centered, threaded bore 82. The plug ispositioned at approximately the middle of the center tube, equidistantfrom each end. Once it is so located, a hole 84 through the wall of thecenter tube 76 and a radial bore 86 in the insert are aligned. A pin(not shown) is then placed within the hole and bore to fixedly positionthe two elements.

A left end cap 88 (FIG. 7) is specifically designed for the proximal endof the electrode. The cap, formed of PVC or other insulatingcomposition, has an outer end wall 90 having a plurality ofcorona-minimizing circular grooves 92 and an outer side wall portion 94of cylindrical configuration and of somewhat greater diameter than theouter diameter of the outer tube 60. The wall portion 94 also includes aplurality of the grooves 92. The rightmost end of the outer side wallportion 94 terminates in a shoulder 96 which defines one side of a deepradial groove 98. The groove 98 supports a sealing system for theelectrode 20. The groove 98 is defined by shoulder 96 and, at its otherend by wall 100 which, with opposed shoulder 102, defines a circularstep portion 104 whose outer diameter approximates the inner diameter ofthe outer tube 60. A third step portion 106 is of lesser diameter thanthe inner diameter of the outer tube 60. This step portion bears aseries of radial bores, such as bore 108 seen in FIG. 7, which pass thepressurized air into the space between the outer tube 60 and siliconetube 68, as will be discussed. The end cap 88 terminates at its interiorend with fourth and fifth step portions 110, 112, each of lesserdiameter than its predecessors. Fourth step 110 is of a diameter chosento contact and support the inner surface of the silicone tube 68, whilefifth step 112 similarly supports the inner surface of the end of centertube 76. An O-ring 164 in radial groove 114 in the step 112 seals thecenter tube to the cap.

The outer and center tubes 60 and 76 are preferably of nickel-platedaluminum. The outer tube may have an outer diameter of 2 inches with a0.065 inch wall thickness, while the inner tube is of 0.058 inch wallthickness and a 1.5 inch outer diameter. The silicone tube is of nominal0.095 wall thickness, with a 1.5 inch inner diameter. The length of theouter tube is 17.125 inches, the outer tubes being sized proportionally.

A sealing system located within the groove 98 includes a generallyL-shaped silicone gasket 116, one leg 124 of which occupies a part ofthe groove. The remainder of the groove is filled by an O-ring 118. Thegasket 116 has a notch 120 located at the intersection of the legs 122,124 of the "L", whose width is chosen to firmly grip the end of theouter tube 60. The O-ring 118 and the gasket 116 form a sufficientlytight seal to prevent leakage of any ozone enriched air from theelectrode.

In order to permit the passage of air into the space defined between theouter tube 60 and the silicone tube 68, a longitudinal bore 126 in thecap 88 passes in from its outer end wall 90. The bore has a threadedportion 128 to accept a mating connector.

As seen in FIG. 9, the bore 126 connects with a series of transversebores in the end cap, each of which terminate at the stepped portion106. Bore 126 intersects with chordal throughbore 130 having opposedends 132, 134 and perpendicular radial bore 108 bearing end 136 as seenin FIG. 7. The chordal bore 130 also joins with the ends of a pair ofparallel chordal bores 138, 140 perpendicular thereto, whose distal endsform yet another pair of exits 142, 144. Accordingly, the bores 108,130, 138, and 140 provide a series of passageways connected to bore 126and which all terminate in the stepped portion 106 to provide anentranceway path for the air entering the electrode. While a single holeor any arrangement of holes will introduce the air into the intra-tubeair gap 74, we have found that arrangement as disclosed herein appear topresent an optimal introduction of air to the gap. In particular, suchintroduction occurs with the diameter of exits 132, 134 and 136 being0.0625 and diameter with exits 142, 144 being 0.1875 inch diameter.

The end cap 88 further includes a main throughbore 146 in which acylindrical, rod-supporting insert 148 (FIG. 7), preferably made ofteflon, is placed. Passing inwardly from the distal end wall 150 of theinsert is a blind bore 152 which communicates with concentricthroughbore 154. The end wall 150 of the insert is aligned with the endwall 90 of the end cap 88 to present a smooth, substantially common endsurface. This alignment may be maintained by a pin 156 passing throughaligned radial throughbore 158 in the cap 88 and blind bore 160 in theinsert 148. An appropriate notch (not seen may be placed in the end ofthe center tube 76 to provide clearance for the pin.

Positioned at the right end of the outer tube 60 is a right end cap 162and associated elements. It is identical to the left end cap except thatit is rotated about the longitudinal axis of the electrode so that it isin a position 180° opposite the position of the left end cap. Thus, theexit ports 130, 132, 136, 142 are in opposite and inverted orientationto those in the left end cap. The ozone-enriched air passes out of theelectrode exits through these opposite locations. Ozone is generated bythe creation of a high-voltage electrical field between the center andouter tubes 60 and 76.

Current is introduced into the electrode by a pair of central electricalconnecting rods 166, 166' which extend between the two end caps andwhich are joined together at the plug 80, best seen in FIG. 12. Each ofthe rods are provided with first threaded end portions 168 which matewith the threaded bore 82 in the plug. The rod 166 extends through theteflon insert 148 of left cap 88, as seen in FIG. 7, to provide anelectrical connection terminal. Its distal end includes a threadedportion 170 which passes out through the blind hole 152 and beyond theend wall 150. The rod 166 is maintained in proper position by washer andnut assembly 172. A threaded end seal 174, preferably of teflon andhaving a central bore for the rod is then placed within the blind hole,leaving the end of the rod exposed for electrical contact. The rightside rod 166' is somewhat shorter than the left rod, such that itterminates within the blind hole 152 in the right side cap, as shown inFIG. 8. Its threaded end 176 is similarly affixed with a washer and nutassembly 172, the blind hole at this end being capped by solid threadedteflon cap 178. The outer tube 68 serves as the opposed electricalconnection for the electrode, it being mounted in a conventional mannerin an electrical connector which also serves as the holder for theelectrode.

Another feature of the present invention is a series of safety deviceswhich protect the system and allow the system to operate in a remotelocation, preferably proximate the water tower. Among the features thatallow this to occur are a plurality of safety control systems. . Turningto FIGS. 3 and 4, the first feature is an air pressure safety switch180. As air is the raw material for ozone production, an insufficientairflow lessens or halts ozone production and can result in unnecessarywear and perhaps damage to the electrode dielectric. Furthermore, theair dryer 36 will not work properly if there is an insufficient supplyof compressed air coming into the system. Accordingly, air pressuresafety switch sensor 180 is located on the air supply conduit justbefore the compressed air enters the pressure regulator unit 40. If theair pressure sensor reads an air pressure of less than 30 psi, thesystem will automatically shut down, and will not restart until the airpressure sensor reads a pressure of 30 or more psi. In addition to thesystem shutting down, an alarm is energized by means of a light or anaudible sound in order to alert an operator that there is a problemwithin the system.

The second safety feature is vacuum switch 182. A sensing line 186connects to the output conduit 44 from the electrodes 20. If the switchdoes not read a vacuum of approximately 20 inches of mercury, it is anindication that the venturi 52 has shut down. If this occurs, the switchautomatically turns off the system. The lack of the proper vacuumsuggests that the pump inlet filter is clogged, the lines to the towerare blocked, or the pump 22 has shut down for some reason. The switchwill therefore shut the whole system down until such time as the alarmcondition has been cleared. In the case of a drained-down tower, thesystem will sense the absence of water and thus automatically protectthe ozone generator and treatment system.

The next safety feature is the door switch 188 (FIG. 4). The panel 12provides access to the electrodes 20 as seen in FIG. 1. If this door isopen, switch 188 opens. As there is high voltage present in thegenerator cabinet, the door switch minimizes the risk exposure of aperson to such voltages.

Positioned upstream of the air pressure sensor 180 is pressure sensor192 FIG. 3) which monitors the operation of filters 32, 34, and 38. Afilter discharge pressure drop on the outport line from after-filter 38to a predetermined level, such as 80 psi, indicates that one or more ofthe filters may be plugged or otherwise not be functioning properly.Therefore, this pressure sensor is set to trigger an alarm before alarm180 operates. When this alarm sounds, the filters can be checked to makecertain they are working properly. This may require routine maintenanceof filter elements. With a further reduction in pressure, sensed byalarm 180, the system will shut down.

The next safety feature is the solenoid valve 194 in electrode outputline 44. If the system shuts down for any reason, the solenoid valvewill automatically close the conduit. This prevents water which mightback up from the venturi system into line 44 from reaching theelectrodes. The valve will remain in its closed state until such time asthe alarm condition has been removed.

The next safety feature is an emergency stop switch 196 (FIG. 4) whichincludes a large actuator 198 on the front panel of cabinet 14 of theunit 10 as seen in FIG. 1. Depressing the switch removes electricalpower from the entire system. In addition, an electrical disconnectmounted at the rear of the main cabinet removes all power to permit safeinspection and maintenance of the unit.

The final safety system operates in conjunction with the oxidationreduction potential probe 200, whose operation will be discussed infrain connection with ORP controller 202, shown in FIG. 14. When the userfirst initiates operation of the system the oxygen-reduction potentialof the water is typically at an unsatisfactory level, which wouldnormally cause the system to enter an alarm state as issued bycontroller 202 passing a signal to sensor interface 206. A bypassoverride switch 210 allows the alarm to be overridden during thisinitial period. The controller will allow the generation of ozone at themaximum level until the oxidation-reduction potential in the tower waterreaches an acceptable level. Once the system is operating within thedesired parameters, the bypass switch is turned to the normal position.The alarm system is then operative.

After the initial phase, when the sampling probe 200 senses a drop inORP in the water coming from the water tower to a point below the alarmset point, the alarm system will be triggered, subject to a programmed1.5 hour delay. Sometimes a significant amount of an organic contaminantwill be introduced in the water, such as leaves being blown into anopen-top water-tower during a windstorm. Under these conditions thesystem has to be given time to increase its ozone production tocompensate for the additional impurities. If, after an hour and a halfthe ORP has not reached the proper level, the alarm system will set offa visual and/or audible alarm at 208. The system will continue tooperate, however. If the alarm is not answered in an additional twohours then the system will shut down although the alarm will continue toremain active.

A watchdog portion of controller 202 compares consecutive ORP readings.In the event of a fouled or dirty probe, the ORP readings will remainconstant for an extended interval, such as 1 hour. In such a case, analarm signal is sent to a chosen remote location on an RS 422 or 232interface, while ozone output is automatically reduced to zero.Similarly, if the ORP probe fails, the controller will send anappropriate signal, while halting ozone production as required.

Description of Electrical Circuitry

Electrical power comes into this system through Lines L₁, L₂ whichprovide 240-volt, single-phase power, each 120 volts to ground orneutral L_(o). In order to protect the system against power surges, acircuit breaker 212 is positioned at the entrance to the electricalsystem. One hot leg, such as L₁, carries each of the switch/sensors, inseries, such that each sensor can control the system.

Power is supplied through line L₁ to main contactor relay 214, whichcontrols the application of full 240 volts to the pump 22, systemcooling equipment 216, and to invertor 218 which powers the bank ofelectrodes 20. The differential pressure switch 192 activated by thethree filters 32, 34, 38 is not in series with the contactor, as itsactivation does not result in a system shutdown. Upon a pressure drop ofthe predetermined amount the switch 192 is activated, sending an alarmsignal to sensor interface circuit 206. This results an audible orvisual alarm at 208. If the failure escalates pressure sensing switch180 becomes energized, causing system shutdown.

Invertor 218 provides the high voltage AC required for operation of theelectrodes. As shown in FIG. 5, the invertor utilizes a 0-1 volt dcoutput from controller to provide a nominal 0-220 volt output. The inputis directed to a comparator 220, which compares the input to a referencevoltage generated by converter 222 which senses the output of theinvertor. Comparator 220 generates an error signal output which is usedto vary the amplitude of a 870 hz signal produced by oscillator 224.After appropriate filtering at 226, the control signal is applied topulse width modulator 228, which modulates a rectified 220 volt input inbridge circuit 230. The output on lines 232, 234 is a variable 0-220volt ac signal at 870 hz. It has been found that optimal oxygen-ozoneconversion occurs at this frequency of applied voltage.

The output of invertor 218 on lines 232, 234 may be monitored byammeter-voltmeter pair 236 and protected by circuit breaker 338. Thevoltage drives high voltage transformer 240, having a nominal 10,000volt output at 220 volt input, its high voltage output being used toenergize the electrodes 20.

The control voltage for the invertor 218 is generated by ORP controller202, whose input is generated by oxygen-reduction potential sensingprobe 200, which is of known construction, as exemplified by theSensorex model S220CD. The output of the probe varies in a range ofapproximately 0-1000 mV, depending primarily on the ozone concentrationof the sample, although other constituents, primarily chlorine, mayaffect its value. Chlorine, however, is short-lived, and in a recyclingsystem where the water is not substantially replenished, the ORP readingis a significant indicator of ozone concentration. The probe output isutilized by the controller to place the control voltage on lines 242,244 which corresponds to an invertor output of between approximately 90and 180 volts, inversely proportional to the probe output. In general,an output voltage of approximately 125-150 volts across the transformer240 primary is required to generate ozone, depending on the specificflowrate and construction variables. Thus, an invertor output of 90volts corresponds to a virtual zero ozone output.

The controller 202 of the present invention, depicted in FIG. 14, is amicroprocessor-driven unit which interfaces the ORP probe and invertorand provides the control mechanism for operation of the ozone-producingelectrodes. In particular, the microprocessor CPU 246 is provided withan appropriate interface 248 with the ORP probe, whose output istypically a 0-1000 mv dc signal. A keypad 250 for programming andentering data, is also provided. The CPU 246 also controls main digitaldisplay 254, which displays the ORP value sensed by the probe 200, a setpoint display 256, which indicates the targeted ORP and statusindicators 258 which set forth the condition of the controller. An alarmrelay output 260 provides ORP-derived alarm signals to the audio and/orvisual alarms 208 through sensor interface 206, while auxiliary relaycontrol output 262 allows a remote alarm output to be provided. Inaddition, the controller includes an RS-422 or equivalent interface 264which allows interconnection with a telephone line. The controller isconfigured as known in the art, using appropriate programs stored inread-only memory 266 and/or programmable readonly memory 268.

In addition to display of the ORP and setpoint readings, the controllercalculates the 0-1 volt output at control output 270 provided toinverter 218. Ozone output is inversely proportional to ORP, ascontaminants lower the ORP to below the desired level.

Typically the ORP of water is in the range of 0-1000 mV, and it has beendetermined that an ORP of 650 mV resulting from ozonation provides anoptimal level of organic oxidation. Thus, a setpoint in the range of 650mV is chosen.

Alarm override switch 210 provides the alarm disable signal to preventan alarm upon start-up. An appropriate status indicator 258 willindicate the override mode, as well as the alarm condition overridden.Setpoint switch 272 activates the watchdog system to guard againstsustained constant ORP probe readings which might indicate probeproblems. The system can be activated or disabled as desired. Theelectrodes are designed to operate at a transformer 240 primary currentof 7.5 amps, which yields an ozone output of 30 grams/hr. By providingmultiple electrodes, sufficient ozone production may be reached for anysize cooling tower.

The controller is provided with operating power through 120v supplysystem 274, which is connected to line L₁ (FIG. 4) before the safetysystem such that it remains powered in the event of a system shutdown.This allows an appropriate alarm signal to be generated as required.While the sensor switches 180, 182, 188 and 196 are not connecteddirectly to the controller, the operation of any of these switches,which leads to system shutdown, will have a prompt effect on the ORPsensed by the probe 200. This will result in an out-of-range conditionbeing sensed by the controller, which will then activate the appropriatealarm outputs.

We claim:
 1. An apparatus for controlling the condition of cooling towersystem water, comprisingone or more ozone generator electrodes havinginner and outer concentric electrode tubes, a concentric dielectric tubetherebetween creating an annular space between said dielectric tube andouter electrode tube for the passage of oxygen-containing air forconversion of a portion of said oxygen to ozone and first and secondopposed end caps for supporting said electrode tubes and dielectric tubein a concentric orientation and for the entry of air into and exit ofozone-containing air from said annular space; means for providing dry,filtered input air at a depressed dewpoint and at constant flowrate tothe first end caps of said electrodes; sensor means for determining theoxidation-reduction potential of a water sample obtained from thesystem; means coupled to said sensor means and to said ozone generatorelectrodes for maintaining the oxidation-reduction potential of saidcooling tower system water at a target level in the range of about 550to 6750 mv by comparing the determined oxidation-reduction potentialwith said target value and controlling the production of ozone inresponse thereto to allow the generation and maintenance of containmentoxidation by-product secondary biocides at an elevated level; means forcombining the ozone produced by said electrodes with a portion of saidcooling tower system water for return of resulting ozonated water to thesystem for introduction of the ozone thereto; and means for monitoringthe flow of said input air and the output of said electrodes whereby analarm condition is indicated if said flow or output depart fromestablished parameters.
 2. The apparatus of claim 1, wherein said flowmonitoring means comprise at least one pressure responsive sensor. 3.The apparatus of claim 2, whereby said monitoring means and said sensormeans comprise a microprocessor.
 4. The apparatus of claim 3, whereinsaid monitoring means includes means for overriding said alarm conditionupon system start-up.
 5. An apparatus for controlling the condition ofcooling tower system water by variable ozonation to maintain the levelof intermediate biocides at a desired elevated level, comprisingmeansfor monitoring the oxidation-reduction potential of at least a portionof the cooling tower system water; ozone-generating means for generatingozone and introducing said ozone generated into said water; and controlmeans coupled to said monitoring means and said ozone-generating meansfor maintaining the oxidation-reduction potential of said water at atarget level in the range of about 550 to 650 my to promote thegeneration and maintenance of secondary biocides by adjusting theproduction of ozone by said ozone-generating means in a continuousmanner in response to the oxidation-reduction potential sensed by saidmonitoring means.
 6. The apparatus of claim 5, wherein said controlmeans is adapted to maintain the oxidation-reduction potential in therange of 550 to 650 mV.
 7. An apparatus for fostering the developmentand maintenance of secondary biocides in the water of a recirculatingcooling water system, comprisingconduit means for removing a portion ofthe cooling water from the system for ozone treatment and returning thetreated water to the system for blending with the contents thereof;means for monitoring the oxidation-production potential of said removedportion prior to the ozone treatment thereof; electrode means forgenerating ozone from the oxygen of ambient air passed through theelectrode means, the output of said electrode means including saidgenerated ozone; control means coupled to said monitoring means and saidelectrode means for maintaining the oxidation-reduction potential ofsaid cooling system water at a target level in the range of about 550 to650 mv to maximize the generation and maintenance of intermediatebiocide products of the oxidation of water contaminants by adjusting theproduction of ozone by said electrode means in response to theoxidation-reduction potential value sensed by said monitoring means; andmeans for combining at least a portion of said removed portion ofcooling system water with the ozone-containing output of said electrodemeans.
 8. The apparatus of claim 7, wherein said electrode means areconnected to a voltage source of approximately 860 hz.
 9. The apparatusof claim 8, wherein the ozone production level of said electrodes isvaried by adjusting the voltage applied to said electrodes.
 10. Thesystem of claim 9 including means for providing ambient air to saidelectrodes at a constant flow rate.
 11. The apparatus of claim 7 furthercomprising means for passing said ambient air through said electrodemeans at a constant rate, and means for providing a varying voltage tosaid electrode means to control the ozone concentration of the output ofsaid electrode means.
 12. The apparatus of claim 11, wherein saidcontrol means is coupled to said electrode means by way of said meansfor providing a varying voltage.
 13. The apparatus of claim 7, whereinsaid control means comprises means for adjusting the production of ozoneas a function of the difference between the oxidation-reductionpotential monitored by said monitoring means and said target level. 14.The apparatus of claim 13, wherein said control means further includesmeans to adjust the production of ozone in a continuous manner.